Electrical printing using stencil and moving slot powder metering means



March 7, 1967 R. B. BOOHER 3,307,477

ELECTRICAL PRINTING USING STENCIL AND MOVING SLOT POWDER METERING MEANS Filed Sept. 25, 1964 7NVENTOI2 7 16. 2 RICHARD B. BOOHER United States Patent ELECTRICAL PRINTING USING STENCIL AND MOVING SLOT POWDER METER- ING MEANS Richard B. Booher, Perrysbnrg, Ohio, assignor to Owens-Illinois, Inc, a corporation of Ohio Filed Sept. 25, 1964, Ser. No. 399,138 (Ilaims. (Cl. 101114) This invention relates to methods and apparatus for electrical printing of articles, and more particularly to methods and apparatus in which printing powder particles are electrically transferred from a supply through stencil screens to the article surface.

The invention is especially concerned with those processes in which a stencil screen is interposed between a supply of powder particles and an article surface to be decorated, and electric potentials are applied to the article, screen and powder supply to charge the powder particles and electrically attract them to the article surface. In transit between the supply and article surface, the particles pass through openings in the stencil screen.

In one early technique, the foregoing process was per formed by supporting a supply of printing powder particles upon the upper surface of the stencil screen and locating the article in vertical registry beneath the screen. In this particular arrangement, the stencil screen mesh was relatively fine, as compared to the particle size and, during the transfer of the powder, a brush was employed to brush the particles through the screen.

In other types of processes, the stencil screen was placed above a prepared bed of powder, and the article was positioned above the screen.

In the brushing process described above, the mesh of the stencil screen must be relatively fine, as compared to the particle size, because otherwise an uncontrolled amount of particles would pass through the screen, posing problems in bringing the article to and from registry beneath the screen. This requirement in turn further necessitates the use of some means for assisting the particles to pass through the fine screen mesh and, hence, the brushing operation is employed. The amount of or number of particles expressed through such a screen by a brushing operation can be controlled only approximately, thus introducing variations in shading and density of the powder images applied to the article. Further, the brushing operation inherently tends to produce some scattering of particles, resulting in fuzziness along the image edges. Finally, for best results, at least two or three strokes of the brush completely across the image defining areas of the stencil are required, thus imposing limitations on the number of operations possible Within a given amount of time.

In the second type of process described above, preparation and frequent replacement of beds of powder particles in the supply are required, due to the fact that a reasonably precise relationship between the surface of the supply and the stencil screen must be observed. In many processes of this type,the number of powder transfers from a given bed is limited in that the transferring operation tends to pack the particles remaining in the bed. Further, the process inherently requires that each operation removes a certain amount of powder from the prepared bed.

Accordingly, it is an object of the present invention to provide methods and apparatus for applying a patterned layer of powder particles to an article surface in which a powder supply is available for a large number of successive operations and in which preparation or handling of the supply between successive operations is not re quired.

It is another object of the invention to provide methods and apparatus for electrically applying a patterned layer of printing powder particles to an article surface in which a large volume supply of powder particles is supported above a stencil screen independently of the screen.

Other objects and features of the invention will become apparent by reference to the following specification and to the drawings.

In the drawings:

FIGURE 1 is a schematic side elevational view, partially in section, of apparatus embodying the present invention; and

FIGURE 2 is a plan view with certain parts broken away or omitted, showing the relationship between the slotted plate and stencil screen.

Referring to FIGURE 1, a supply of printing powder particles designated generally 10 is supported in a bin 12 whose bottom is defined by a wire mesh screen 14 which overlies a sliding plate 16. A stencil screen 18 having pattern-defining apertures, such as 20, is supported in a horizontal position by any suitable means, not shown, in spaced, vertical registry beneath bin 12 and in spaced, vertical registry above the surface of an article A which is to be decorated. Article A is in turn supported upon an electrically conductive base 22.

Stencil screen 18 preferably takes the form of a relatively fine wire mesh which is coated so that the mesh openings are closed. Pattern-defining apertures 20 are formed by removing the coating from the desired areas of the mesh to leave apertures of the desired pattern, the apertures being crossed by the wire mesh of the screen. For further details of such screens, and methods of preparing them, reference may be had to United States Patent No. 3,100,150.

The printing powder particles in supply 10 may take the form of any of several commercially available powders supplied for this purpose. The particles are graded as to size, and the particle size preferably falls within a size range which is relatively small compared to the dimensions of the openings in screen 18. Preferably, the maximum particle size is chosen to be smaller than the mesh opening by a factor of at least 10, and preferably more. Screen 14 is preferably chosen to be of a mesh size equal to that of stencil screen 18 to assure that particles dispensed from bin 12 can easily pass through the mesh openings in the pattern or image apertures of stencil screen 18.

Plate 16 is suitably supported for horizontal sliding movement beneath bin 12 as by brackets 23 on the bin and is formed with an elongate slot 24. The length of slot 24 is selected in accordance with the overall dimensions of the apertures 20 in stencil screen 18. Plate 16 is supported for horizontal movement in a direction perpendicular to the longitudinal dimension of the slot, as indicated by arrow B in the drawing. The plate may be driven in sliding movement by any suitable means such as a pneumatic motor, schematically indicated at P.

The apertures 20 in stencil screen 18 may be thought of as lying completely within a rectangular area on the screen, indicated at R in FIGURE 2. The longitudinal extent of slot 24 is selected to extend parallel to and to equal or exceed the length of one side 26 of the rectangular area. The length of stroke of movemnet of plate 16 is selected to be at least equal to the length of side 28 of the imaginary rectangular area R. Thus, upon horizontal movement of the plate to carry slot 24 from one side of bin 12 to the other, slot 24 completely sweeps above the imaginary area in which the image apertures 20 are located.

Upon movement of plate 16 to pass slot 24 underneath bin 12, particles are dispensed from the supply 10 in a stream having a cross sectional area corresponding to that of slot 24. To electrically charge and attract particles from supply to the surface of article A, electric potential sources illustrated schematically at V1 and V2 are respectively connected to the article supporting plate 22 and to powder bin 12. In a typical instance, screen 18, because it is formed of a wire mesh, is electrically grounded as are the respective power supplies. Plate 22 is indicated as being connected to a positive terminal, while a negative charge is being applied to powder in bin 12. The specific polarity is not of importance as long as the polarity of the powder supply is opposite that of the article surface to establish an electric field extending from the screen to the article surface which is oriented to attract and guide the particles to areas on the article corresponding to the image apertures in screen 18. With the indicated connections, the negatively charged powder particles dispensed through slot 24 are both gravitationally and electrically attracted to the surface of the article A and those particles which pass through apertures fall upon areas of the article surface corresponding to the shape of the image apertures.

Because the powder in bin 12 is in a loose mass, handling or preparation of the powder between successive operations is not required, since the powder merely gravitationally sinks to the bottom of bin 12. By regulating the transverse width of slot 24 and the speed at which plate 16 is moved horizontally, an accurately regulated amount of powder can be transferred during each operation.

While I have described one embodiment of my invention, it will be apparent to those skilled in the art that the disclosed embodiment may be modified. Therefore, the foregoing description is to be considered exemplary rather than limited, and the true scope of the invention is that defined in the following claims.

I claim:

1. The method of applying a patterned layer of powder particles capable of being electrically charged to the surface of an article comprising the steps of supporting a supply of powder particles in spaced vertical registry above a stencil screen having pattern-defining apertures therethrough with the supply of particles disposed over an area completely overlying the pattern apertures in said screen, positioning an article in spaced vertical registry beneath the pattern apertures of said screen, applying electric potentials of opposite polarity to said article and the particles in said supply, releasing a stream of charged particles from a first region of said supply constituting a relatively small portion of the total area over which the supply is disposed, and continuously shifting the region of said supply from which the stream of particles is released to traverse said stream across the pattern-defining apertures of said screen.

2. The method of applying a patterned layer of powder particles capable of being electrically charged to the surface of an article comprising the steps of supporting a supply of printing powder particles upon the upper surface of a horizontal plate at one side of an elongate slot in said plate, positioning a stencil screen having patterndefining apertures therethrough in spaced relationship beneath said plate with said apertures located in vertical registry with said supply of particles, positioning an article in spaced vertical registry beneath said screen, applying electric potentials of opposite polarity to said article and the particles in said supply, and shifting said plate horizontally while maintaining said supply of particles against horizontal movement to move said slot from one side of said supply to the other to release a stream of charged particles from said supply and traverse said stream across the pattern-defining apertures of said screen.

3. The method of applying a patterned layer of powder particles capable of being electrically charged to an article surface comprising the steps of locating an article surface in spaced vertical registry beneath a horizontal stencil screen having pattern-defining apertures therethrough lying within a given rectangular area on said screen, supporting a plate having an elongate slot therethrough of a length greater than one side of said rectangular area in spaced parallel relationship above said screen in a first position wherein said slot is located in parallel vertical registry with said one side of said rectangular area, moving said plate horizontally from said first position into vertical registry with the opposite side of said rectangular area while continuously dispensing a stream of electrically charged printing powder particles downwardly through said slot, and while moving said plate establishing an electric field extending from said screen to the surface of said article oriented to electrically attract and guide the charged powder particles through the apertures of said screen to the areas of the article surface corresponding to the pattern-defining apertures of said screen.

4. Apparatus for applying a patterned layer of powder particles capable of being electrically charged to an article surface comprising a powder supply bin adapted to contain a supply of powder particles, a sliding plate defining the bottom of said bin and having an elongate slot for discharging particles from said bin in a stream having a narrow elongate horizontal cross sectional configuration, a horizontal stencil screen having pattern-defining apertures therethrough located below said bin, said apertures lying within a rectangular area on said screen one side of which extends parallel to said slot and is of a length equal to or less than the length of said slot, means for locating an article surface to which a patterned layer is to be applied in spaced vertical registry beneath the apertures of the screen, electric potential means for electrically charging particles and for simultaneously establishing an electric field extending from said screen to the article surface with the article surface charged to a polarity opposite to the polarity of the charged particles, and means for sliding said plate horizontally across the bottom of said bin in a direction normal to the longitudinal extent of said slot to sweep a stream of charged particles discharged through said slot laterally across said rectangular area of said screen.

5. In an electrical printing method wherein a conductive screen having a plurality of apertures over a portion thereof defining the area to be printed is positioned in spaced relation opposite the surface of the article to be printed, said screen being in an electric circuit to establish an electric field extending from the screen to the article surface, the steps of providing a source of powder particles of a particle size small enough to pass through the apertures of said screen at the side of the screen opposite the surface of the article to be printed, placing a barrier defining an elongated, narrow slot between the screen and source of powder particles thereby permitting powder particle movement onto the screen only through said elongated slot, moving powder particles from the source toward the screen through said slot of the barrier, and causing movement of the elongated slot relative to the screen and along the screen to sweep the apertured area of the screen thereby introducing powder particles into said electric field through the apertured printing areas of the screen, whereby the powder particles are deposited on the article surface in the pattern of an image defined by the apertured area of the screen.

6. The method defined by claim 5, wherein said source of powder particles is connected in an electric circuit and the powder particles thereof are electrically charged in said circuit to a polarity to attract them to said screen.

7. Apparatus for applying a patterned layer of powder particles capable of being electrically charged to an article surface comprising a pattern forming stencil screen including apertures therethrough defining a two dimensional pattern, means for supporting an article to be print ed with its surface in spaced registry with the apertures of said screen, means defining a slot extending across one dimension of the two dimensional apertured area of the screen and disposed on the side of the screen opposite the article surface, means for supplying powder particles to said slot for dispensing onto said screen across said one dimension thereon, means for relatively moving said slot with respect to said screen and article surface across the second dimension of said two dimensional apertured area of the screen, and means for establishing an electric field extending from the screen to the surface of the article and oriented to electrically transfer particles from the apertures of the screen to areas of the article surface opposite and corresponding to the pattern apertures of the screen.

8. The apparatus defined by claim 7, wherein the means for establishing the field comprises an electric potential means for charging powder particles supplied to said slot and establishes simultaneously the electric field from the screen to the article surface with the field oriented so that the article surface has a polarity opposite the polarity of the charged particles.

9. In apparatus for electrically printing a surface with particles of a printing powder, an electrically conductive screen having open areas corresponding to the printing portion and masked areas corresponding to the non-printing portion, a voltage supply source, means for electrically connecting a material to be printed upon to said voltage supply source, means spacing said screen from physical contact with the material to be printed upon, thereby forming an air gap therebetween, means for connecting said voltage supply source in circuit with said screen for creating an electrical potential difierence between the screen and the material to be printed upon thereby establishing an electric field in the said air gap therebetween, the improvement comprising means for applying printing powder onto the surface of the screen opposite the material to be printed, said means including an element defining an elongated slot extending transverse the open areas of the screen, a supply of printing powder including particles of a size to pass freely through the open areas of said screen and connected to supply said powder particles to and through said elongated slot and to the screen, and means for relatively moving the slot-defining element and the screen and the material to be printed upon a distance in a direction normal to said slot sufficient to completely sweep the open areas of the screen and thereby successively apply said powder particles to the screen for passage through the open areas of the screen for transfer across said air gap in the electric field.

10. The apparatus of claim 9, wherein a conductive element is in contact with the powder particles of said supply and provided with a voltage supply source, and means for connecting said voltage supply source to the screen and said conductive element so that said particles are charged to an electrical polarity opposite the electrical polarity of the material to be printed.

References Cited by the Examiner UNITED STATES PATENTS 2,919,170 12/ 1959 Epstein.

3,081,698 3/1963 Childress.

3,124,482 3/1964 Olden 118637 3,202,092 8/ 1965 Childress.

3,202,093 8/1965 Childress.

ROBERT E. PULFREY, Primary Examiner. E. S. BURR, Assistant Examiner. 

1. THE METHOD OF APPLYING A PATTERNED LAYER OF POWDER PARTICLES CAPABLE OF BEING ELECTRICALLY CHARGED TO THE SURFACE OF AN ARTICLE COMPRISING THE STEPS OF SUPPORTING A SUPPLY OF POWDER PARTICLES IN SPACED VERTICAL REGISTRY ABOVE A STENCIL SCREEN HAVING PATTERN-DEFINING APERTURES THERETHROUGH WITH THE SUPPLY OF PARTICLES DISPOSED OVER AN AREA COMPLETELY OVERLYING THE PATTERN APERTURES IN SAID SCREEN, POSITIONING AN ARTICLE IN SPACED VERTICAL REGISTRY BENEATH THE PATTERN APERTURES OF SAID SCREEN, APPLYING ELECTRIC POTENTIALS OF OPPOSITE POLARITY TO SAID ARTICLE AND THE PARTICLES IN SAID SUPPLY, RELEASING A STREAM OF CHARGED PARTICLES FROM A FIRST REGION OF SAID SUPPLY CONSTITUTING A RELATIVELY SMALL PORTION OF THE TOTAL AREA OVER WHICH THE SUPPLY IS DISPOSED, AND CONTINUOUSLY SHIFTING THE REGION OF SAID SUPPLY FROM WHICH THE STREAM OF PARTICLES IS RELEASED TO TRAVERSE SAID STREAM ACROSS THE PATTERN-DEFINING APERTURES OF SAID SCREEN. 